A cleaning method for cleaning soiled items will be described for the case of a dishwasher for cleaning kitchen and dining ware items. As shown in FIG. 7, a conventional dishwasher employs a method of spraying water particles of wash water to items to be cleaned, e.g. dishware, in advance to make food debris stuck on the dishware fully swell and then removing the swollen food debris by using, for example, a mechanical power of jetting out wash water or chemical operations of detergent (see, for example, Japanese Patent Laid-open Application No. 2000-189375). Hereinbelow, a configuration of such a conventional dishwasher will be described. Main body 51 of the dishwasher includes therein washer tub 53 having a rack (not shown) for arranging dishware therein, and door 54 is provided at opening 52 of washer tub 53. Installed inside washer tub 53 are nozzle 55 for ejecting out wash water in washer tub 53 toward the dishware and spray arm 56 for generating water particles of the wash water in washer tub 53.
The operation of the dishwasher with the above-described configuration will now be explained. Further, cleaning operational mechanism of food debris stuck on the surface of, e.g., dishware will be described with reference to FIGS. 8A to 8C. First, after loading soiled dishware into the rack and loading detergent into the dishwasher, the operation of the dishwasher is initiated. Once the operation is started, wash water contained in washer tub 53 is sprayed by spray arm 56, as shown in FIG. 8A, to thereby produce water particles 57. Then, thus generated water particles 57 are dispersed into washer tub 53 to thereby make contact with food debris 59 stuck on the surface of dishware 58 and then permeate into food debris 59, as shown in FIG. 8B. Thereafter, as shown in FIG. 8C, food debris 59 gradually swells due to the permeation of water particles 57 thereinto. Particularly, in case the food debris are of water-soluble substances such as starch, the swelling degree of food debris 59 increases. Afterwards, a main washing for cleaning dishware 58 by using a cleaning fluid jetted out from nozzle 55 is performed. Here, the cleaning fluid refers to a solution containing detergent dissolved therein. The cleaning operational mechanism of the food debris stuck on the surface of the dishware during the main washing process will be described in conjunction with FIGS. 9A to 9C. Food debris 59 swollen in the pre-washing step are gradually washed away from dishware 58 by a great amount of wash water 60 sprayed from nozzle 55, as shown in FIGS. 9A to 9C. Upon the completion of the main washing process, a rinsing process is executed several times by replacing soiled wash water in washer tub 53 with fresh water. Then, by performing a warm-water rinsing process by using fresh warm water heated up to about 70° C., the cleaning of dishware 58 is finished. Finally, a drying process is executed to dry water drops on the dishware, and the operation of the dishwasher is terminated.
In the cleaning method of the conventional dishwasher, however, the pre-washing step is performed just by using tap water that contains no detergent component therein. Thus, though a certain degree of effect of swelling starch debris such as boiled rice may be obtained, improvement of cleaning performance in terms of stubborn protein or oil debris cannot be achieved.